Since the normal human skull is rigid, transient volume variations in intracranial structures, such as cerebral vasculature and brain, cause the intracranial cerebrospinal fluid (CSF) to flow from the cranial vault into the spinal canal. (Mokri 2001). As a result, CSF flows cyclically through the foramen magnum, which connects the cranial vault and the spinal canal.
About 0.7% of the U.S. population suffers from a congenital disorder known as the Chiari I malformation, wherein the cerebellar tonsils are located in the upper cervical spinal canal. In Chiari I patients, the displacement of fluid from the cranial vault is partially obstructed at the level of the foramen magnum, with the result that CSF velocities and pressures in the foramen magnum increase. (Linge 2011). A fraction of Chiari I patients develop complications such headache, or syringomyelia (spinal cord cyst) and motor and sensory deficits.
Craniovertebral decompression is the standard surgical treatment for suitable Chiari I cases and generally Chiari I with syringomyelia. This procedure typically consists of enlarging the foramen magnum and upper cervical spinal canal so as to facilitate the flow of CSF and reduce fluid velocities and pressure gradients. (Linge 2014) In the U.S., surgeons have performed over 10,000 such decompressions annually since 2007 (reference: Labuda, “Chiari Malformation: Treatment,” C&S Patient Edu. Found., 2012). The Academy of Neurologic Surgeons reports 14,131 cases of “Chiari decompression (CPT codes 61343, 61345) in 2011. The procedure in most patients reduces or eliminates the syringomyelia within a few months. Craniovertebral decompression is usually safe and effective but, in one report, one third of patients had complications including vertebral artery injury, spinal cord injury, nerve root injury, suffocation, cerebrospinal fluid leakage, and infection (Barong 2014).
Bermans Iskandar (Iskandar 2004) and Maria Dolar (Dolar 2004) have shown that craniovertebral decompression decreases CSF velocities in the foramen magnum. In theory, the craniovertebral decompression improves CSF flow to alleviate symptoms. But there remain different theories on the mechanism(s) by which decompression achieves therapeutic results.
Other less frequently-used surgical procedures for treating Chiari I patients include CSF shunting, de-tethering of the spinal cord, and marsupialization of spinal cord cysts, generally with complications and/or a lower rate of therapeutic success than decompression. In conventional treatments for this disorder, inserting a catheter is not a highly effective method of treatment and is not based on a well-designed scientific model. Instead, the protocol is simply to remove fluid rather than correct the underlying physiologic abnormality. But the real problem in this condition is the increased amplitude of the cyclic pressure wave.
In contrast, the disclosed invention consists of an implantable, biocompatible, and Magnetic Resonance (MR) compatible device (where non MR compatible elements may be readily removed before any MR testing). The disclosed invention functions as a chamber that effectively varies in size as CSF pressure changes, decreasing as CSF pressure increases and increasing as CSF pressure decreases, by utilizing passive compliant as well as active compliant members to modulated CSF pressure fluctuations and to modify related CSF flow. Placed within the CSF fluid spaces of the cranial vault, the disclosed device, in various embodiments, effectively diverts spinal fluid flow from the foramen magnum and damps cyclic CSF pressure pulsations related to the cardiac cycle. This diversion of flow diminishes cyclic CSF fluid flow in the foramen magnum, which is theoretically the cause of spinal cord cysts in Chiari patients. Including instrumentation to measure the pressure values over time may also provide diagnostic information and measure of the condition. The instrumentation also monitors the function of the device, monitors intracranial pressure fluctuations and determines the need for a changing the volume of the chamber in the device.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.